Rotors of the above type must turn at very high speeds of 25,000 to 60,000 RPM, which poses very serious problems for the construction of the support bearings. There are generally utilized ball bearings of small size whose interior ring or race is mounted on a fixed hollow axle for the rotor and whose exterior ring is mounted in a bore of the rotor, such that the rows of balls and their cages rotate at a very high speed and are subjected to a substantial centrifugal force which produces deformations and abnormal wear. Furthermore, the chamber containing the rotor is subjected to a suction, necessary to the process, but which has the disadvantage of aspirating, through the ball bearing, external dust which fouls and causes wear of the ball bearing. In order to avoid this entry of dust, these rollers are generally lubricated by means of an oil mist under pressure, but then a substantial part of the oil is found on the fiber filaments while the remainder is evacuated into the suction source. By maintaining the bearing chamber under pressure a great consumption of air is effected. Finally the rotor is driven by a belt whose tension produces a constant force on the same side of the interior ring of the bearings which constitutes a condition of use which is unfavorable and rapidly leads to wear of the bearing.